1896.] BRITISH HYDROIDS AND MEDUSZ. 481 
Banks to be unusually luminous, flashing in many parts like 
lightning. He directed some of the water to be hauled up, in 
which he discovered ....a large species of medusa, to which he 
gave the name pellucens. The Medusa pellucens measures about 
six inches across the crown or umbrella.” 
This is clearly from the figure and description a Scyphomedusa. 
Shaw (1812) has copied the figure given by Macartney. 
Lesson (1843) has not only given Thaumantias hemispherica as a 
distinct species, but also Vhaumantias lucida, Macartney. Amongst 
the synonyms of the latter Lesson has placed Medusa scintillans 
(=Noetiluca scintillans) and Medusa pellucens (=Banks’s Scypho- 
medusa), but in the description of the species he only gives 
Macartney’s description of Medusa lucida. Haeckel apparently 
has copied from Lesson, without referring to the original papers, 
as he has placed as synonyms under Vhaumantias hemispherica 
both Medusa scintillans and Medusa pellucens. 
Forbes (1848) next described Thaumantias hemispherica. It is 
first, however, important to consider Forbes’s views upon the 
value of sense-organs or marginal vesicles for the identification of 
the species. 
. Forbes, in 1841, gave the following advice on the identification 
of species belonging to the genus Zhaumantias :— 
“‘ 1st. The number of tentacula (always a multiple of four). 
2nd. The presence, absence, size, and colour of the eyes at 
their bases. 
érd. The colour of the cross-vessels and proboscis. 
4th. The shape of the umbrella. 
5th. The shapes of the clubs of the vessels. 
6th. The form and lobation of the oral proboscis or peduncle. 
“‘T have mentioned these sources of character in what I conceive 
to be the order of their respective importance, but all should if 
possible be noted.” 
I may here say that Forbes’s statement that the tentacles are 
always a multiple of four is not correct. The multiple system is 
also adopted by Haeckel, and it leads to the assumption that 
Meduse have a most wonderful symmetry. The statement holds 
good up to thirty-two tentacles, but above that number the 
tentacles, when carefully counted, show odd as well as even 
numbers. I found, out of 47 mature specimens of Obelia lucifera, 
only two specimens showing an equal number of tentacles in each of 
the quadrants, and only nine specimens possessing a number that 
could be equally divided by four. Twenty-six specimens have an 
even number of tentacles, and 21 specimens an odd number. 
Forbes included in his genus Thaumantias several Meduse which 
have since been transferred to other genera, viz. :— 
Thaumantias pilosella (= Euchilota pilosella). 
Thaumantias lucifera (= Obelia lucifera). 
Thaumantias melanops (=Traropsis multicirrata). 
All these have certain characteristic features by which they may 
Proc. Zoo. Soc.—1896, No. XX XI. 
